In ball joints used in steering or suspension systems of automobiles, lubricants are sealed in. Lubricants known for such use include a composition containing Duomeen T dioleate as a base oil and a diamide compound (JP-62-54155-B), a composition containing a urea-base compound as a thickener and polyethylene wax, paraffin wax, microcrystalline wax, and/or a fatty acid amide wax (JP-2-194095-A), and a composition containing a base oil or a wax mixed with an amidoamine compound and a fatty acid salt for inhibiting fluttering during high speed driving (JP-6-240274-A).
These compositions exhibit excellent low friction at ordinary temperatures, which property is required for ball joints, but cannot maintain the property in higher and lower temperature ranges, causing increased friction.
With recent progress in automobile technologies, temperature in the engine compartment has been remarkably rising, which requires lubricants for ball joints to exhibit low friction in a higher temperature range. On the other hand, opportunity to use lubricants for ball joints in cold regions has also been increasing, which requires the lubricants to exhibit low friction in a lower temperature range as well.